Metal-complexes consisting of the particular metals and particular coordination molecules show various properties depending on the combination of the kind of metals and the kind of the coordination molecules. These materials have a wide range of applications, for example, drugs, luminescent materials, coating medium, etc. On the other hand, ultrafine particles are not merely made fine from bulk solids, but they often drive a novel character that never appears in the bulk. Such an appearance of the novel characters has extensively been studied and used. For example, semiconductor or metal fine particles show various properties depending on their particle sizes. A stained glass owes its multiple colors to metal ultrafine particles. In addition, the fine particles of a magnetic oxide such as ferrite have been already put into practical use in, for example, DNA analysis. However, synthesizing ultrafine particles of the metal complexes have been started only in this decade.
Among the metal-complexes, Prussian blue and its analogues (Prussian blue-type metal complex), have extensively been studied. Prussian blue has used as a blue pigment from the past. Furthermore, it has been studied as a potential material for applications of displays and biosensors. FIG. 35 shows the crystal structure of the Prussian blue-type metal complex. The structure is relatively simple, and is such that two kinds of metal atoms (metal atoms 221 (MA) and metal atoms 224 (MB) in FIG. 35) assembling NaCl-type lattices are three-dimensionally crosslinked with cyano groups (carbon atoms 222 and nitrogen atoms 223). As the metallic atoms, various elements such as vanadium (V), chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), iron (Fe), ruthenium (Ru), cobalt (Co), nickel (Ni), platinum (Pt), copper (Cu) can be used. Because various character such as magnetism, electrochemistry, or optical responsiveness by the substitution of the metallic atoms, various kind of materials has been studied (referring to Patent document 1, Patent document 2).
The production of fine particles from the Prussian blue-type metal complex plays an important role in an attempt to put the metal complex into practical use. The production can thus improve the dispersibility of the metal complex in a solvent. As the dispersibility improves, an inexpensive film formation method such as spin coating can be employed, so a biosensor or the like can be produced at a low cost. In addition, the metal complex can be processed by employing any one of the various printing methods, so the metal complex can be expected to find applications in, for example, display devices. Such materials as described below have been reported as magnetic materials: a material that expresses its magnetism at room temperature; and a material the magnetism of which can be regulated by an external stimulus such as irradiation with light or the application of a pressure. The materials are assumed to find use in a wide variety of applications when the materials are turned into nanoparticles. Investigations have been conducted on the application of the magnetic nanoparticles of oxides to memory devices and biomaterials, and the Prussian blue-type metal complex is also assumed to find use in the same applications.
There have been a few reports of the method to produce ultrafine particles of Prussian blue-type metal complex. In these reports, as the materials for stabilizing ultrafine-particles, a surface active agent such as a di-2-ethylhexylsulfosuccinate sodium salt (AOT), a polymer as poly(vinylpyrrolidone (PVP), or a protein such as ferritin (referring to Non-patent document 1) were employed, a molecular having a relatively low molecular weight such as oleylamine (Patent document 3). However, most of those stabilizing molecules each involve the utilization of an organic solvent such as toluene as a solvent. In contrast, water is often a suitable solvent in actual applications. This is because of the following reason: attention must be paid to an influence of the organic solvent on a human body and the handling of the organic solvent, so a special apparatus may be needed. When water can be used as a solvent, such problems can be solved, and the solvent can be handled even in, for example, an environment like an ordinary house. The following example has been reported (Patent document 3): a water-soluble aminoethanol is utilized as a protecting molecule in order that the metal complex may be dispersed in water. However, the water-soluble aminoethanol may be difficult to handle owing to its basicity, and the Prussian blue-type metal complex hydrolyzes, with the result that the yield in which the metal complex is produced reduces in some cases.
In addition, the following example has been reported (Non-patent document): Prussian blue is produced by adding an excessive amount of part of synthesis precursors. However, this example does not qualify for large-scale synthesis because the yield of Prussian blue product is low, and it becomes too much trouble to perform a process for purifying Prussian blue. In addition, only the particles each having the following characteristic are obtained: the internal structure of the particle is entirely uniform. Accordingly, the resultant particles can find use only in a narrow range of applications. In addition, a production method called a layer-by-layer method has been adopted in the production of a thin film from Prussian blue to be applied to a device, so steps for the production become complicated. Further, in the case of this method, a homogeneous film cannot be produced because the method involves alternately laminating the Prussian blue particles and another material.
[Patent document 1] JP-A-2005-3679 gazette
[Patent document 2] JP-A-7-270831 gazette
[Patent document 3] JP-A-2006-256954 gazette
[Non-patent document 1] M. Yamada et al.: J. Am. Chem. Soc., Vol. 126, 2004, p 9482.
[Non-patent document 2] D. M. Delongchamp et al. Chem. Mater., Vol. 16, 2004, p 4799